1. Field of the Invention
This invention pertains generally to configuration Read Only Memory (ROM) implementations. More particularly, the invention is directed to a system and method for providing a dynamic configuration ROM using double image buffers for use with serial bus devices.
2. The Prior Art
In serial bus architecture, a node is an addressable entity (i.e., a logical entity with a unique address), which can be independently reset and identified. The address space provided by a node can be directly mapped to one or more units. A unit is a logical entity, such as a disk controller, which corresponds to unique I/O (input/output) driver software. On a multifunction node, for example, a processor and I/O interfaces can be different units on the same node.
Nodes can be interconnected using an appropriate physical topology suitable for use with the serial bus, such as a backplane environment and/or cable environment, for example. These environments are described in further detail in Institute of Electrical and Electronics Engineers (IEEE) Standard 1394-1995 xe2x80x9cIEEE Standard for a High Performance Serial Bus,xe2x80x9d published Aug. 30, 1996 which is incorporated herein by reference. Interconnected nodes may reside in either environment without restriction.
Configuration ROM implementations are well known in the field of serial bus devices and provide the hardware and software specifications of a serial bus node and its associated units. For example, in IEEE Standard 1394, two configuration ROM formats are supported: minimal and general. The minimal ROM format provides a 24 bit company identifier. The general ROM format provides additional information in a bus_info_block and a root_directory. Entries within the root_directory may provide information or may provide a pointer to another directory (root-dependent directory and/or unit_directory), which has the same structure as the root_directory. Entries within the root_directory may also provide a pointer to a leaf, which contains information. The unit_directories contain information about the units associated with the node, such as their software version number and their location within the address space of the node, for example.
FIG. 1 shows a general ROM implementation format for IEEE Standard 1394. The ROM directory structure is a hierarchy of information blocks, where the blocks higher in the hierarchy point to the blocks beneath them. The location of the initial blocks (info_length, crc_length, rom_crc_value, bus_info_block, and root_directory) are fixed. The location of the other entries (unit_directories, root and unit leaves, and vendor dependent information) varies according to each vendor, but are specified by entries within the root_directory or its associated directories.
In general, the bus_info_block provides specific information about the node. For example, the bus_info_block may indicate whether the node carries out isochronous data transfers. Additionally, the bus_info_block provides a node_vendor_id field, a chip_id_hi field, and a chip_id_lo field, among other things. Together, the node_vendor_id, chip_id_hi, and chip_id_lo fields forms a 64-bit node unique identifier. Other node specific information may be provided in the root_directory and the root leaves of the ROM. Unit specific information is normally provided in the unit_directory and the unit leaves of the ROM. For example, the specification identification and the version number may be provided for a particular protocol in the unit_directory and the unit leaves. IEEE Standard 1394-1995 xe2x80x9cIEEE Standard for a High Performance Serial Bus,xe2x80x9d published Aug. 30, 1996, describes the general ROM format and its associated blocks in further detail and is incorporated herein by reference.
The configuration ROM is published to other nodes on the bus. That is, nodes on the bus may access some known address space on any node to read or otherwise ascertain that node""s configuration ROM information at any time. Certain nodes (management entities) that carry out the operation of controlling other nodes proactively ascertain the configuration ROM information contained in other devices on the bus.
Originally, configuration ROM implementations were intended to be static and unchanging. As such, the configuration ROM information image provided to the other nodes on the bus remains fixed during the operation of the node. However, it may be desirable to scale the capabilities of a node while the node is already operational. For example, a node may want to provide an additional protocol service or an additional unit device, for example. However, the addition of a protocol or a unit device, in the above example, would require modification of the configuration ROM in order to publish the availability of the new unit architecture represented by the added protocol or unit device. Similarly when an existing software service (a protocol service, for example) is removed from the node, the configuration ROM would need to be updated to publish the unavailability of the removed software service.
Traditionally, changing or modifying the configuration ROM while xe2x80x9cactivexe2x80x9d and available to the other nodes on the bus may result in inconsistent configuration ROM data. This inconsistency may result when, for example, a node is reading the ROM while the ROM is being updated. The requesting node may read the incorrect rom_crc_value, for example, because unit directories and unit leaves are being added for the newly added unit architecture. Thus, it would be a disadvantage to update or modify an active configuration ROM available to the other nodes on the bus.
In order to scale a node (i.e., add or remove a unit for the node) according to the prior art, the node would have to be unlinked from the serial bus. Once unlinked from the serial bus, the configuration ROM is unavailable to the other nodes. Updates can then be made to the configuration ROM of the unlinked node without the risk of publishing inconsistent ROM data to the other nodes, as described above. After ROM update, the node can then link back to the serial bus and republish the newly updated configuration ROM information.
Accordingly, there is a need for a system and method for providing a dynamic configuration ROM which may be updated while inked to the serial bus and without risk of providing inconsistent configuration ROM information to the other nodes on the bus. The present invention satisfies these needs, as well as others, and generally overcomes the deficiencies found in the background art.
An object of the invention is to provide a system and method for providing a dynamic configuration ROM which overcomes the deficiencies in the prior art.
Another object of the invention is to provide a system and method for providing a dynamic configuration ROM in a node device wherein the configuration ROM may be updated while the node is active and linked with other devices.
Another object of the invention is to provide a system and method for providing a dynamic configuration ROM in a node device which provides double ROM image buffers, one of which is active and the other of which is modifiable.
Another object of the invention is to provide a system and method for providing a dynamically modifiable configuration ROM in a node device which provides services to publish the dynamically modifiable configuration ROM.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing the preferred embodiment of the invention without placing limitations thereon.
The present invention is directed to a system and method for providing a dynamic configuration ROM that may be updated while active and linked to the serial bus. The system and method of the present invention allow the update of the configuration ROM without the risk of publishing inconsistent configuration ROM information to the other nodes on the bus. The system and method of the invention relate to machine-readable media on which are stored embodiments of the present invention. It is contemplated that any media suitable for retrieving instructions is within the scope of the present invention. By way of example, such media may take the form of magnetic, optical, or semiconductor media. The system and method of the invention also relate to data structures that contain embodiments of the present invention, and to the transmission of data structures containing embodiments of the present invention.
In its most general terms, the invention comprises configuration ROM software executing within a local node which provides services to modify the configuration ROM of a node and services to publish the modified configuration ROM. The software is executed by a conventional processor within the serial bus device as is known in the art. While the illustrative embodiment is described herein using IEEE Standard 1394 topology, the invention is suitable for use with other topologies including those complying with IEEE Standard 1212, for example.
The invention provides first and second configuration ROM images. The ROM images are provided in random access memory (RAM) within the local node. The first ROM image is initially set as the xe2x80x9cactivexe2x80x9d ROM and contains the configuration ROM entries for the node as well as currently operating units, if any. The second ROM image is initially set as the xe2x80x9cupdatexe2x80x9d ROM and is, although not required, normally empty. The xe2x80x9cupdatexe2x80x9d ROM is where new and/or updated entries to the config ROM will be constructed. During operation the invention sets the second ROM to xe2x80x9cactivexe2x80x9d and the first ROM to xe2x80x9cupdatexe2x80x9d, and vice versa according to algorithm set forth in the invention as described further below. The invention xe2x80x9ctracksxe2x80x9d the active ROM by, for example, providing a pointer to the xe2x80x9cactivexe2x80x9d ROM.
The invention publishes the currently xe2x80x9cactivexe2x80x9d configuration ROM to the other nodes on the serial bus. In operation, when a node on the serial bus queries the local node for its configuration ROM, the local node provides the entries from the xe2x80x9cactivexe2x80x9d configuration ROM. The xe2x80x9cupdatexe2x80x9d ROM is not published to other nodes on the bus. Rather the xe2x80x9cupdatexe2x80x9d ROM serves as a xe2x80x9cbufferxe2x80x9d where new and/or updated entries may be constructed, as described further below. For example, new configuration ROM entries may be added by a user via ROM building services. These entries are stored into a data storage structure, such as a database, for example. At the time the user determines that the new and/or updated entries should be published, the invention constructs the modified ROM in the xe2x80x9cupdatexe2x80x9d ROM from the database. After the construction of the xe2x80x9cupdatexe2x80x9d ROM is completed, the entries provided in the xe2x80x9cupdatexe2x80x9d ROM is published to the other nodes on the bus using the publishing means of the present invention as described further below.
The invention provides ROM building services to the higher layers (the application layer, for example) of the local node to add and/or modify entries to the configuration ROM of the node. For example, a software client running in the local node may add ROM entries for a protocol service that was added during the operation of the node. These entries are stored into a data storage structure, such as a ROM database table, for example. A new entry may thus be stored into a new data record of the table. The data record entries in the ROM database may later be constructed into the appropriate configuration ROM format in the xe2x80x9cupdatexe2x80x9d ROM just before publication. In this way, the constructed xe2x80x9cupdatexe2x80x9d ROM will have a new unit directory and new unit leaves to indicate the added protocol""s version number and other pertinent protocol information, for example. Other entries of the xe2x80x9cupdatexe2x80x9d ROM will also be modified from their original values, such as the rom_crc_value and the root_directory, as is known in the art. Similarly, entries in the ROM database may be deleted and/or modified when a service is removed from the node.
These changes to the configuration ROM maintained in the ROM database may be made while the node is active and linked to the serial bus. The local node may continue to provide the configuration information from the information in the xe2x80x9cactivexe2x80x9d ROM, while the ROM database is being modified. Because the data in the ROM database and the xe2x80x9cupdatexe2x80x9d ROM are not published, the risk of inconsistencies in configuration ROM entries provided by the local node is thusly reduced or avoided. Once the modification is complete, the invention provides services to publish the modifications made to the ROM database on the serial bus.
The invention provides services to construct the xe2x80x9cupdatexe2x80x9d ROM from the ROM database and to publish modification made to the xe2x80x9cupdatexe2x80x9d ROM. During the process of publishing modified information, the invention carries out several operations. First, the invention constructs the xe2x80x9cupdatexe2x80x9d ROM using the proper configuration ROM format from the data in the ROM database. In the present example, the configuration ROM format is that described in FIG. 1. Next, the invention switches the states of the configuration ROM images. For example, if the first ROM is currently set as xe2x80x9cactivexe2x80x9d and the second ROM is currently set as xe2x80x9cupdatexe2x80x9d, the invention sets the first ROM as xe2x80x9cupdatexe2x80x9d and the second ROM as xe2x80x9cactivexe2x80x9d. If, on the other hand, the first ROM is currently set as xe2x80x9cupdatexe2x80x9d and the second ROM is currently set as xe2x80x9cactivexe2x80x9d, the invention sets the first ROM as xe2x80x9cactivexe2x80x9d and the second ROM as xe2x80x9cupdatexe2x80x9d.
Immediately after the states of the configuration ROM images are switched, the invention signals or otherwise initiates a bus reset. In IEEE Standard 1394 following a bus reset occurs, the nodes on the bus, among other things, may rescan the bus and re-read the configuration ROM address space of the local node. Since the xe2x80x9cactivexe2x80x9d ROM now contains the modified entries for the configuration ROM of the local node, the local node now is presented as having the newly modified (added or removed) services. As noted above, certain nodes (management entities) that carry out the operation of xe2x80x9ccontrollingxe2x80x9d other nodes proactively ascertain the configuration ROM information contained in other devices on the bus. With the present invention, these controlling nodes are able to recognize and make use of the newly available capabilities of the modified node.
Further modifications can be made to the ROM database, as described above, and the process of publishing such additional modifications to the local node""s configuration ROM is repeated.